Species splitting increases estimates of evolutionary history at risk Marine Robuchon, Daniel Faith, Romain Julliard, Boris Leroy, Roseli Pellens, Alexandre Robert, Charles Thévenin, Simon Veron, Sandrine Pavoine To cite this version: Marine Robuchon, Daniel Faith, Romain Julliard, Boris Leroy, Roseli Pellens, et al.. Species splitting increases estimates of evolutionary history at risk. Biological Conservation, Elsevier, 2019, 235, pp.27- 35. 10.1016/j.biocon.2019.03.041. hal-02183563 HAL Id: hal-02183563 https://hal.sorbonne-universite.fr/hal-02183563 Submitted on 15 Jul 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Biological Conservation 235 (2019) 27–35 Contents lists available at ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon Perspective Species splitting increases estimates of evolutionary history at risk T ⁎ Marine Robuchona,b, , Daniel P. Faithc, Romain Julliarda, Boris Leroyb, Roseli Pellensd, Alexandre Roberta, Charles Thévenine, Simon Vérona,d, Sandrine Pavoinea a Centre d'Ecologie et des Sciences de la Conservation (CESCO), Muséum national d'Histoire naturelle, CNRS, Sorbonne Université, 57 rue Cuvier, CP 135, 75005 Paris, France b Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Muséum national d'Histoire naturelle, CNRS, IRD, Sorbonne Université, Université Caen-Normandie, Université des Antilles, 57 rue Cuvier, CP 26, 75005 Paris, France c The Australian Museum Research Institute, The Australian Museum, Sydney, New South Wales 2010, Australia d Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum national d'Histoire naturelle, CNRS, EPHE, Sorbonne Université, Université des Antilles, 45 rue Buffon, CP 50, 75005 Paris, France e Institute of Ecology and Environmental Sciences (iEES), Sorbonne Université, CNRS, INRA, IRD, Place Jussieu, 75005 Paris, France ARTICLE INFO ABSTRACT Keywords: Changes in species concepts and the rapid advances in DNA-based taxonomy and phylogeny of the past decades Cryptic species have led to increasing splits of single species into several new species. The consequences of such splits include Extinction risk the delineation of post-split species that may have restricted ranges and potentially increased extinction risks. ExpPDloss Species splitting also leads to a re-evaluation of phylogenetic trees, with post-split trees having more species, but HEDGE species that are less evolutionarily distinctive compared to pre-split trees. Such changes in extinction risks and Phylogenetic diversity distinctiveness may influence strategies for the conservation of phylogenetic diversity (PD). In this study, we Prioritization strategies evaluated the effect of splitting a species into two sister species on two widely used measures toevaluate PD at risk: (i) the expected loss of phylogenetic diversity associated with a set of species and, (ii) for each species, the gain in the expected phylogenetic diversity if the species is saved from extinction. We developed theoretical predictions and then explored these in a real-world case study of species splitting in the Rhinocerotidae family. Species splitting increases both of our measures related to PD at risk, implying underestimation of PD at risk when valid species splitting is not recognised. This bias may lead to suboptimal conservation decisions: the subset of species or sites given priority for conservation may be different from the subset that actually deserves priority conservation attention. We discuss how our findings can be applied to more complex studies andthe perspectives this highlights for accommodating new taxonomic knowledge in conservation strategies. 1. Introduction species number observed in the last 30 years has two main non-mu- tually exclusive origins. The first one is the ‘taxonomic inflation’ (Isaac The number of described species has increased rapidly over the last et al., 2004) due to the shift from the historical biological species 30 years. For instance, the number of mammal species rose from 4629 concept (BSC; Mayr, 1963) to the more recent phylogenetic species in the second edition of Mammal Species of the World (MSW2; Wilson concept (PSC; Cracraft, 1989). Under the BSC, species are defined as and Reeder, 1993) to 6495 in the recent work of Burgin et al. (2018), reproductively isolated taxa. Under the PSC, a species is the smallest set corresponding to an increase of ca. 40% in 25 years. While the dis- of organisms that share an ancestor and that can be distinguished from covery of undescribed forms in the field or in collections has con- other such sets by at least one character; such phylogenetic species are tributed to augment the number of described species, most of this in- not necessarily reproductively isolated and it can be difficult to know crease has resulted from species splits (Collen et al., 2011; Burgin et al., where to draw the line between species, notably if different datasets 2018). Species splits linked to the evolutionary nature of species result suggest different species delimitations. The number of species diag- from speciation events, which may be directly observed by scientists nosed under the PSC tends to be greater than under the BSC (Agapow such as the rapid hybrid speciation recently documented in Darwin's et al., 2004). The second reason for the increase in species splits is finches (Lamichhaney et al., 2018). However, the drastic increase in taxonomic progress (Sangster, 2009). Indeed intensified naturalist ⁎ Corresponding author at: Centre d'Ecologie et des Sciences de la Conservation (CESCO), Muséum national d'Histoire naturelle, CNRS, Sorbonne Université, 57 rue Cuvier, CP 135, 75005 Paris, France. E-mail address: [email protected] (M. Robuchon). https://doi.org/10.1016/j.biocon.2019.03.041 Received 4 September 2018; Received in revised form 20 March 2019; Accepted 27 March 2019 Available online 09 April 2019 0006-3207/ © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). M. Robuchon, et al. Biological Conservation 235 (2019) 27–35 exploration coupled with rapid advances in DNA-based taxonomy and often an important time lag between the description of newly-delimited phylogeny reconstruction incorporating fossil information allowed in species resulting from the splitting of a species and the widespread the past decades the discovery of a large number of cryptic species uptake of these newly-delimited species. Consequently, the conserva- (Bickford et al., 2006) and a rapid increase in the resolution and tion status of split taxa may remain under-estimated for years (e.g. availability of time-calibrated phylogenies (Diniz-Filho et al., 2013). Groves et al., 2017). We thus need robust mechanisms to reconcile Together with species lumping and the discovery of truly undescribed conservation policies with the rapidly evolving taxonomic knowledge forms, species splits are thus the results of taxonomic revisions which (Raposo et al., 2017; Thomson et al., 2018). formulate hypotheses about what species are and to which entities they Species splitting has another key consequence for the conservation correspond in nature. Depending on the species concept and/or the of threatened evolutionary history: it is expected to decrease the ED methods used in such taxonomic revisions, the hypothetical species component of the species' scores. Arguing that any increase in extinc- produced may differ, therefore creating taxonomic uncertainty. tion risk due to species splitting is balanced by a decrease in ED, Isaac Many conservation policies depend on species extinction risk and et al. (2007) found that EDGE scores for existing mammal species were endemism and/or on species numbers. Consequently, they rely on our robust to species splits. However, Isaac et al. (2007) used species names ability to identify and name species (e.g. Agapow et al., 2004). Initially, to calculate EDGE scores, whereas the correspondence between a spe- the International Union for the Conservation of Nature (IUCN, 1980) cies name and the set of individuals it represents in nature is altered in also considered taxonomic distinctiveness as a factor relevant to con- case of species splitting: a same species name may not represent the servation priorities because “the size of potential genetic loss is related same set of individuals before and after split. In addition, the effect of to the taxonomic hierarchy”. Extending these ideas to the broader species splitting may differ between EDGE and HEDGE scores because preservation of evolutionary history, Faith (1992) developed a critical only the HEDGE approach acknowledges the fact that the magnitude of biodiversity measure called “phylogenetic diversity” (PD), and asso- the evolutionary history at risk from any one species naturally depends ciated calculations of PD gains and losses. Integrative PD-based scores on the fate of its close relatives (Faith, 2008). for species priority-setting have been developed (e.g. Isaac et al.,